1. Field of the Invention
The present invention relates to a zoom lens barrel assembly, and in particular, to a multi-stage-extension zoom lens barrel assembly having a lens barrier.
2. Description of the Related Art
There are concurrent needs to increase magnification of camera zoom lenses and to miniaturize them. For this reason, modern zoom lenses are constructed as a multi-stage-extension zoom lens barrel assembly. A multi-stage-extension zoom lens barrel assembly employs a helicoid structure or a cam structure to connect barrels and allow them to move relative to one another. Although the cam structure permits a high degree of freedom in terms of how much a lens barrel can extend outwards for a predetermined rotation angle of the barrel, it is difficult to ensure rigidity and light-blocking performance of the lens barrel with this structure. However, the helicoid structure ensures rigidity and light-blocking performance of the lens barrel although this structure allows the lens barrel to extend outward only by a fixed amount for a predetermined rotation angle of the barrel. For this reason, the helicoid structure is considered more suitable for use in multi-stage extension lens barrel assemblies.
A typical zoom lens barrel assembly includes a lens barrier on the frontmost end thereof. This lens barrier is opened and closed by making use of relative movement between the frontmost barrel having the lens barrier and an adjacent barrel. When there are many stages (sub-barrels) in a barrel assembly, however, the relative displacement between the lens barrels may become too small to provide sufficient stroke length required for the opening/closing of the lens barrier. In particular, in the case of a wide-angle zoom lens, in which the optical system has a small length at the wide-angle extremity, displacement of the lens barrel assembly from its retracted position, where the length of the barrel assembly and thus the length of the optical system are smallest, to the wide-angle extremity is small. If helicoid structures are used in such a zoom lens barrel assembly, leads of the helicoids of each barrel need to be close to each other in order to effectively make use of the length of the zoom lens barrel. This makes displacement of each lens barrel substantially equal to one another. As a result, sufficient stroke length required for the opening/closing of the lens barrier cannot be achieved.
To cope with above problems, only the frontmost lens barrel is constructed to have a cam structure so that the frontmost lens barrel extends outward by a larger amount for a small rotation angle and causes the other lens barrels to extend only by a small amount. While sufficient stroke can be achieved, the lead for advancing the frontmost lens barrel to open the lens barrier becomes too large. This can cause too large a resistance when the lens barrel is retreated, which affects the strength of the lens barrel. In addition, if only the frontmost lens barrel extends outward by a large amount, tension is undesirable exerted on a flexible printed board, which connects a shutter unit mounted on the frontmost lens barrel to a circuit board in a camera body.
As an alternative approach, the other lens barrels that are connected to the frontmost lens barrel can be each constructed to have a cam structure in order to provide a section or sections that allow the zoom lens barrel to extend outward only by a small amount, or do not extend outward at all, when the barrels are rotated. In this construction, the sufficient stroke length for the opening/closing of the lens barrier is provided within a rotation range between the retracted position and the wide-angle extremity. Such cam structures, however, make it difficult to ensure sufficient rigidity of the zoom lens barrel assembly. It should be noted that the rearmost lens barrel cannot be constructed as a cam structure since the driving force needs to be transmitted through gears to the first lens barrel.
In view of the above-described drawbacks of the conventional lens barrel assemblies, the present invention provides a novel zoom lens barrel assembly structure that not only enhances the rigidity of multi-stage-extension zoom lens barrel, but also provides a sufficient stroke length needed for the opening/closing of a lens barrier.
For example, a zoom lens barrel assembly is provided, including a plurality of lens barrels including a rearmost lens barrel, secured to a camera body, and a frontmost lens barrel. At least two adjacent lens barrels, of the plurality of lens barrels arranged between the camera body and the frontmost lens barrel, are connected to each other via a helicoid structure. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The helicoid structure allows the at least two adjacent lens barrels to rotate and move in an optical axis direction relative to each other while the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. At least a portion of the helicoid structure includes a slip region which allows the at least two adjacent lens barrels to rotate without relatively moving along the optical axis.
A barrier mechanism can be provided on the frontmost lens barrel, the barrier mechanism being opened and closed via movement of the frontmost lens barrel in the optical axis direction as the zoom lens barrel assembly moves between the retracted position and the minimally extended position, and by relative rotation of the at least two adjacent lens barrels via the slip region.
It is desirable for the first adjacent lens barrel connected to the frontmost lens barrel via the cam structure to be connected to a second adjacent lens barrel via a second helicoid structure which causes the connected the first and second adjacent lens barrels to rotate and move along the optical axis relative to each other as the zoom lens barrel assembly moves from the retracted position to the minimally extended position, the second helicoid structure also including a slip region which allows the first adjacent lens barrel and the second adjacent lens barrel to rotate without relatively moving along the optical axis.
In another embodiment, a four-stage-extension zoom lens barrel is provided, including a first barrel connected to a fixed barrel secured to a camera body, the first barrel being movable so as to retreat and advance relative to the fixed barrel; a second barrel connected to the first barrel; a third barrel connected to the second barrel; a frontmost fourth barrel connected to the third barrel; wherein the first, second, and third barrels are each supported, and are movable in an optical axis direction, via a helicoid structure. The frontmost fourth barrel and the third barrel are connected to each other by a cam structure so as to be movable in an optical axis direction. A barrier mechanism is provided on the frontmost fourth barrel. The helicoid structures for moving the second barrel and the third barrel in the optical axis direction each allow the second and the third barrels to rotate and relatively move in the optical axis direction as the zoom lens barrel moves between a retracted position and a minimally extended position for a photographing operation, each the helicoid structure having a slip region which allows the second and third barrels to rotate without relatively moving in the optical axis direction. The barrier mechanism is opened and closed by a relative movement of the third barrel and the frontmost fourth barrel in the optical axis direction as the slip sections allow the second and the third barrels to rotate.
It is desirable for the fourth barrel to be connected to the third barrel via the cam structure so that the fourth barrel moves in the optical axis direction relative to the third barrel without rotating, and the barrier mechanism to be opened and closed by the relative movement of the third barrel and the fourth barrel in the optical axis direction in the slip section of the third barrel.
It is desirable for the slip section of the helicoid structure of the second barrel to have a different slip angle than the slip section of the helicoid structure of the third barrel.
The helicoid structure having the slip section can include a female helicoid formed on one of two adjacent barrels of the first through third barrels and a male helicoid formed on the other of the two adjacent barrels, and the female helicoid can include a helicoid slip region that permits rotation of the male helicoid when the two adjacent barrels are in a retracted position.
In another embodiment, a zoom lens barrel assembly is provided, including a plurality of lens barrels including a rearmost lens barrel secured to a camera body, and a frontmost lens barrel. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The first adjacent lens barrel is connected to a second adjacent lens barrel via a helicoid structure so that the first and second adjacent lens barrels relatively rotate and relatively move in the optical axis direction as the zoom lens barrel assembly moves between a retracted position and a minimally extended position for a photographing operation, the helicoid structure including a helicoid slip region which allows the first and second adjacent lens barrels to relatively rotate without relatively moving along the optical axis. The helicoid structure having the helicoid slip region includes a female helicoid formed on one of the first and second adjacent lens barrels and a male helicoid formed on the other of the first and second adjacent lens barrels. The female helicoid includes a helicoid slip region which permits rotation of the male helicoid when the first and second adjacent lens barrels are in the retracted position. A circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region.
The helicoid structure having the helicoid slip region and the circumferential groove can constitute a helicoid ring, the helicoid ring being formed by injection-molding a plastic material into a mold.
In another embodiment, a zoom lens barrel assembly is provided, including a pair of lens barrels connected to each other via a helicoid structure, the helicoid structure including a helicoid slip region which allows the pair of the lens barrels to relatively rotate without relatively moving along the optical axis. The helicoid structure having the helicoid slip region includes a female helicoid formed on one of the pair of lens barrels and a male helicoid formed on the other of the pair of lens barrels. The female helicoid includes the helicoid slip region which allows rotation of the male helicoid when the pair of lens barrels are in a predetermined position. A circumferential groove is formed along each of opposing thrust surfaces of the helicoid slip region of the female helicoid.
In another embodiment, a zoom lens barrel assembly is provided, including a plurality of lens barrels, at least two lens barrel of the plurality of lens barrels including a helicoid structure for allowing one lens barrel of the at least two lens barrels to rotate and extend and retreat as the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. The helicoid structure includes a helicoid slip section for allowing the one lens barrel to rotate without relatively moving along the optical axis, the helicoid structure including a female helicoid formed on one of the at least two lens barrels and a male helicoid formed on the other of the at least two lens barrels, the male and the female helicoids including a helicoid slip region that allows the at least two lens barrels to rotate and prevents the at least two lens barrels from moving along the optical axis when one of the at least two lens barrels is retracted into the other. An eccentricity-preventing member provided on the at least two lens barrels for allowing the at least two lens barrels to slidably and closely engage with each other so as to slide circumferentially and slide in the optical axis direction, the eccentricity-preventing member guiding rotation of the at least two lens barrels via the helicoid slip section when one of the at least two lens barrels is retreated and slightly advanced with respect to the other of the at least two lens barrels.
The eccentricity-preventing member can be formed as a flange which extends circumferentially and projects radially inward from an inner periphery of one of the at least two lens barrels which is provided outside of the other of the at least two lens barrels, the flange being formed in the vicinity of the helicoid slip section and slidably placed over an outer periphery of an inner lens barrel of the at least two lens barrels.
Each of the plurality of lens barrels arranged between a camera body and a frontmost lens barrel can be connected via the helicoid structure, the front most lens barrel and a first adjacent lens barrel being connected to each other via a cam structure, and wherein the first adjacent lens barrel and a second adjacent lens barrel connected thereto constitute the at least two lens barrels.
A barrier mechanism can be mounted on the frontmost lens barrel, the barrier mechanism being opened and closed by relative movement of the frontmost lens barrel and the first adjacent lens barrel in the optical axis direction as the zoom lens barrel assembly moves from the retracted position to the minimally extended position for a photographing operation.
The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 2001-82089, 2001-82090 and 2001-82092 (filed on Mar. 22, 2001) which is expressly incorporated herein by reference in their entireties.